Personnel working in hazardous environments are advised and often required by regulations to wear Personal Protective Equipment (PPE) to protect them from the negative and injurious effects of the environment in which their activities take place. Among the kinds of situations in which PPE is in order are Emergency Response, Hazardous Materials Handling, and Severe Environmental Conditions.
PPE generally consists of respiratory protection and percutaneous protection. Respiratory protection consists of a variety of masks and filtration systems and/or sources of breathable air. Percutaneous protection consists of garments configured to prevent contact of harmful agents with the skin. When combined, the resulting PPE renders the individual protected more or less sealed in a garment. While such garments typically have check valves to vent gases built up within the garment interior, the check valves do not admit any materials into the suit from the surrounding environment.
In order to provide for the comfort and safety of personnel using PPE, means must be provided for maintaining a habitable thermal environment within the PPE. Failure to do so results in buildup of heat and a resulting uncomfortable—at least, and more often deleterious—heat stress for the individual protected by the PPE.
Various technologies exist or have been investigated to cool portions of the garments worn by the personnel to counter or delay the onset of heat stress. These include phase change vests using Phase Change Materials (PCM), Tethered Systems (TS), and Miniaturized Self-Contained Systems (MSCS) to absorb heat from the body torso. PCM materials such as paraffin, hydrated salts, and ice may be packed or juxtaposed with appropriate garment portions, and these “frozen materials” absorb sensible heat from the body by melting. TS comprise some kind of external refrigeration system to which the personnel is “tethered” by supply lines providing the cooling. MSCS use vapor-compression, thermoelectric, magnetocaloric, pulse-tube, thermionic, and thermoacoustic principles, among others, to provide on board cooling. Field tests of PCM-based systems have not shown them to be effective. Further, there is the need to refreeze the PCM or replace it. While TS are generally quite effective in providing cooling, they severely limit the mobility of the individual being protected, thus limiting the individual's effectiveness and responsiveness in emergency situations. Existing MSCS systems generally rely on battery devices which add weight and generate additional heat load. No technologies in use effectively deal with removal of perspiration, and many do not effectively dissipate heat away from the body.
An effective and efficient PPE cooling system is needed which will provide maximum flexibility and freedom of movement for the wearer. Personnel involved in rescue and other first responder activities are among those who will benefit from such a system.